The present invention relates to a hollow or cavity electrode switch and more particularly to such a switch with an anode, a cathode and at least one opening for a discharge gap in which pressure of an ionizable gas p and electrode spacing d are selected so that the starting voltage of the gas discharge decreases with increasing product p.times.d.
The starting voltage for a given gas discharge gap and its usual graph representation as a function of the product of gas pressure p and electrode spacing d in the ignition characteristic is known to constitute (with due consideration of the ignition probability) an important aid for defining electrical discharge devices. For the determination of the dielectric strength of a given gas discharge gap, a comparison is generally made with an infinitely large plate capacitor and the ignition characteristic of such a configuration. However, the practical form of realization of such discharge gaps has electrodes with finite dimensions. For examining the so-called "far breakdown" region including the voltage minimum which involves the determination of the right branch of the ignition characteristic (Paschen curve), it suffices to arrange two flat rounded plates parallel to each other. The plates can have edges having a so-called Rogowski profile. Such a structural arrangement is unusable for the study of ignition characteristics in the left portion of the Paschen curve, i.e., in the so-called "near breakdown" region, because detour discharges may occur. Such detour discharges can be avoided by an electrode construction with flat plate electrodes which are arranged coaxial to each other; bent away from each other at their edges with a radius of curvature that is small relative to the electrode spacing; to extend along the inner cylindrical insulator surface. Thus, a gap is always formed between the bent-away cylindrical edge region of the electrodes and the inside wall of the hollow-cylindrical insulator. With this design form of a low-pressure gas discharge gap it is possible to determine the ignition characteristic for various rare and molecular gases also in the near breakdown region, i.e., to the left of the minimum of the Paschen curve.
Gas discharge switches which are controlled by a pulsed low-pressure gas discharge are also known. They switch, for example, currents of 10 kA at a voltage of 20 kV. The discharge switch contains an anode and a cathode, which are provided with coaxial openings and are separated from each other at their edges by an annular insulator. For the gas discharge a control system is provided which contains a cage type hollow or cavity electrode which is electroconductively connected with the cathode and hence is at the cathode potential. It embraces the cathode back chamber and separates the latter from the region of a pre-ionization. The gas discharge between the cathode and the anode is started by injection of charge carriers The ignition of the discharge gap occurs in two stages. First a preionization is produced by an auxiliary electrode through a glow discharge. Then a trigger electrode receives a negative igniting pulse. The entry of charge carriers into the hollow electrode is made possible by the fact that the potential of a blocking electrode is set to zero. The discharge is initiated with the entry of the charge carriers into the hollow electrode. Such a device is disclosed in J. Phys. E: Sci. Instr. 19 (1986), The Inst. of Physics, Great Britain, pages 466 to 470.
U.S. Pat. No. 2,900,566 discloses another design for a gas discharge switch, wherein a plurality of electrodes is provided which are arranged coaxial to each other and which form a common discharge channel. Several intermediate electrodes are arranged between the anode and cathode.
The gas discharge switch may also contain several discharge channels which are provided with a common trigger means. This trigger means contains a common hollow electrode which is electroconductively connected to the common cathode. The synchronous ignition of the discharge channels is initiated by charge carriers which enter from a pre-ionization region through holes in the bottom of the cage into the cathode back chamber. Such a switch is disclosed in J. Phys. E.: Sci. Instr. 20 (1987), p. 270 to 273.